The Signature of Black Hole-Neutron Star Binaries David Neilsen - - PowerPoint PPT Presentation

The Signature of Black Hole-Neutron Star Binaries

David Neilsen Brigham Young University HEPRO III, Barcelona, 2011

Collaborators

• Matthew Anderson (Louisiana State University)
• Eric Hirschmann (Brigham

Young University)

• Luis Lehner (Perimeter Institute/U Guelph)
• Steve Liebling (Long Island University)
• Patrick Motl (Indiana University Kokomo)
• Carlos Palenzuela (CITA)

BH-NS Mergers

• Inspiral phase
• Energy scale: 1053 ergs
• Time scale (primordial): 108 years
• Merger phase
• Disruption (inside or outside the ISCO)
• Time scale 10-20 ms
• Accretion phase
• Tidal tails & disk
• Time scale 10-100+ s

Two Roads

• Newtonian or PPN Gravity + Nuclear Physics + Neutrinos
• Rosswog+ (2002, 2005, 2007, 2010), WH Lee+ (2010)
• General relativity + Ideal fluids
• Faber+(2007), Etienne+(2009), Kyutoku+(2010), Duez+(2008),

Chawla+ (2010), Stephens+ (2011)

BH-NS Parameter Space

BH Spin MBH/MNS

Star disrupts inside ISCO Star disrupts outside ISCO

Figure after Duez 2011

HAD

• Full Einstein equations
• MHD with ideal fluid

EOS

• Berger-Oliger AMR

(refine both space & time)

• Truncation error based

refinement using shadow hierarchy

• Distributed with MPI

This slide shows some features of our code. Don’t want to concentrate on that. Draw attention to small portion of grid shown here. Different length scales: (1) stars (2) orbit (3) wave zone Use AMR, but still limited in resolution of stars, compared to SNe.

Black Hole-Neutron

• Black hole
• Mass
• Spinning and non-spinning
• Neutron Star
• Mass
• Polytrope
• Magnetic field
• System
• q=5 and initial separtion 100 km

M = 1.4M⊙ Γ = 2 MBH = 7M⊙ a = 0, a = 0.5 R = 15 km

(Chawla et al., PRL 2010)

BH-NS Snapshots

t=5.9ms t=8.9ms t=13.3ms t=16.3ms t=20.0ms t=27.3ms

a=0.5 and B=1012 G

Magnetic Field in Disk

Gravitational Waves

a=0, B=1012 a=0.5, B=0 & B=1012

Accretion Disk

• BH final spin
• Disk mass

Solid-integrated mass Plus-mass outside ISCO

Text

Dash-bound matter Dot-Dash-4*unbound matter

Mdisk ≈ 1%MNS a ≈ 0.56

Disk Temperature

B=0 Initial B=1012

Accretion Power Law

dM dt ∝ t−5/3

Binaries in Globular Clusters

• Event rates of BH-NS binaries by tidal capture comparable to

primordial binaries(Belczynski et al. 2010)

• ~25% of SGRBs have offsets from host galaxies (Berger 2010)
• Eccentric orbits vs. circular
• Accretion rate for BH-NS on parabolic orbits depends on

impact parameter (Stephens+ 2011; W.H. Lee+ 2010)

• Accretion rate goes as t-5/3

Accretion Rate (GR)

0.0001 0.01 1 100 10000 1e+06 t (s) 1e-10 1e-08 1e-06 0.0001 0.01 1 100

formula1

6.81 6.95 7.22 7.5 formula2

Stephens, East, Pretorius (2011)

Accretion Rate (Newtonian)

• 3
• 2
• 1

1 2 3 4 5 6 7

log10(t [s])

42 43 44 45 46 47 48 49 50 51 52 53

log10(Lacc [erg/s])

DNS 2 x 1.4 DNS 2 x 1.1 DNS 1.1 & 1.6 DNS 2 x 1.2 DNS 2 x 1.3 DNS 2 x 1.5 DNS 2 x 1.6 NSBH 1.4 & 4 NSBH 1.4 & 6 NSBH 1.4 & 14 NSBH 1.4 & 16 NSBH 1.4 & 18

!t

5/3

1 min 1 hour 1 day

Rosswog (2007); see also WH Lee+ (2010)

Caveat Emptor

• Vacuum regions
• “Atmospheric” fluid
• Angular momentum
• Cartesian codes in 3D
• Disk mass & orbit sensitive to nonconservation
• Magnetic fields in MHD
• Initially confined to star
• Treatment in vacuum regions is problematic

(see Lehner’s talk)

Summary

• Binary mergers candidates for SGRBs
• Disk and accretion rates
• Disk masses 0.01 Mo (GR) to 0.1 Mo (N)
• Fallback accretion rate t-5/3 (GR), t-4/3 (N)
• Primordial binaries vs. tidal capture
• Closing the loop on input physics
• GR + nuclear EOS + neutrinos
• Magnetic fields (FFE + MHD)